Pavement markings comprising synthetic polymeric fibers

ABSTRACT

The invention relates to thermoplastic pavement marking compositions comprising synthetic polymeric fibers.

RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisional patentapplication serial No. 60/325279 filed Sep. 27, 2001 and U.S. patentapplication Ser. No. 10/078771 filed Feb. 18, 2002.

FIELD OF THE INVENTION

[0002] The invention relates to thermoplastic pavement markingcompositions comprising synthetic polymeric fibers.

BACKGROUND OF THE INVENTION

[0003] Pavement markings are typically used to delineate the boundariesfor lanes of traffic on a roadway. The marking may extend continuously,such as along the outermost boundaries of the driving lanes, orintermittently, such as between lanes.

[0004] U.S. Pat. No. 4,490,432 relates to a pavement-marking sheetmaterial which comprises a non-crosslinked elastomeric precursor such asacrylonitrile-butadiene polymer; a thermoplastic polymer such aspolyethylene which reinforces the sheet material, e.g., by orientationof the thermoplastic polymer so that the calendered product exhibitsgreater strength downweb than crossweb; and a particulate inorganicfiller, which preferably includes platelet-type fillers such as talc,mica, or magnesium silicate.

[0005] U.S. Pat. No. 5,194,113 (Lasch et al.) relates tothermoplastic-based pavement marking sheets. The marking sheets employ aconformant composite material including: polyolefin a nonreinforcingmineral particulate; and/or a thermoplastic upper surface. Preferably,the sheet's thermoplastic upper surface is embedded with reflectiveelements and/or skid-resistant particles. A solventless process ofembedding particles in thermoplastic pavement marking sheets isdisclosed. Processes for preparing marking sheets are also disclosed.Conformant pavement marking sheets which may be applied in coolerconditions are also disclosed.

[0006] Thermoplastic pavement marking materials are 100% solidscompounds typically containing a thermoplastic polymeric material,pigments, filler and glass spheres. Hot-applied thermoplastic isprepared for road deposition in a melting apparatus where granular orblock material is introduced and heated until the material liquefies attemperatures in excess of 400° F. (204° C.). Alkyd thermoplastics tendto be preferred over hydrocarbon thermoplastic compositions in view ofsuch compositions being oil impervious. Thermoplastic pavement markingshave had limited commercial success in cold climates due to the tendencyof such markings to shatter from the roadway upon impact with asnowplow.

SUMMARY OF THE INVENTION

[0007] It has since been discovered that pavement marking sheets havinga greater strength in one direction (e.g. downweb) versus the otherdirection (e.g. crossweb) tend to result in reduced conformability andreduced shear strength. Accordingly, industry would find advantage inpavement marking compositions that exhibit a similar downweb andcrossweb tear. Further, industry would also find advantage isthermoplastic pavement markings having improved cold temperatureperformance.

[0008] The Applicants have discovered that thermoplastic pavementmarkings can be improved by the addition of synthetic polymeric fibers.

[0009] In one embodiment the invention relates to a pavement markingcomposition comprising synthetic polymeric fibers dispersed within athermoplastic-based polymeric material. The synthetic polymeric fibershave a melt point greater than the polymeric material such that thefibers retain their fiber form.

[0010] In another embodiment the invention relates to a method of makinga pavement marking comprising providing a composition comprising athermoplastic-based polymeric material and synthetic polymeric fibers,heating the composition to a temperature wherein the composition isextrudeable and the synthetic polymeric fibers are unmelted; andextruding the composition on a pavement surface.

[0011] In another embodiment the invention relates to a method of makinga pavement marking comprising dry blending a thermoplastic polymer andsynthetic polymeric fibers, melting and mixing the blend; and extrudingthe blend onto a pavement surface at a temperature less than the meltpoint of the synthetic polymeric fibers. In each of these embodiments,the fibers are preferably randomly dispersed within the polymericmaterial throughout the sheet. Preferred polymeric fiber materialstypically have a melt point greater than about 400° F. (204° C.) such asin the case of polyester, polyamide, polypropylene andtetrafluoroethylene. In a preferred embodiment the marking compositionis sufficiently conformable such that the downweb direction and crosswebdirection has a tear ratio ranging from about 0.7 to 1.3 when measuredaccording to ASTM 1938. In another preferred embodiment that compositionexhibits good cold temperature properties such that the composition doesnot shatter into pieces upon impact at cold temperatures. The amount ofsynthetic polymeric fibers preferably ranges from about 0.2 weight-% toabout 2 weight-%. The composition optionally comprises other ingredientsselected from the group comprising reflective elements, extender resins,fillers (e.g. magnetic fillers), and pigments. The synthetic polymericfibers preferably have a fiber length of at least 6 mm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The pavement marking composition of the invention comprisessynthetic polymeric fibers incorporated into a thermoplastic polymericmaterial. The synthetic polymeric fibers may be thermoplastic orthermosetting. If the synthetic polymeric fibers are comprised of athermoplastic material, such material has a melt point greater than thethermoplastic polymeric material the fibers are incorporated within.This insures, that the synthetic polymeric fibers do not substantiallymelt and thus retain their fiber form. Thus, the synthetic polymericfibers are dispersed randomly three-dimensionally throughout thepolymeric material in the finished marking.

[0013] The composition of the synthetic polymeric fibers is chosen basedon the melt point of the intended thermoplastic-based polymeric materialand/or the intended processing temperature. Typically,thermoplastic-based polymeric materials have a softening point or meltpoint ranging from about 240° F. (116° C.) to about 450° F. (232° C.).For improved cold temperature properties, it is surmised to employsynthetic polymeric fibers that don't fracture at cold temperatures suchas fibers comprised of a material having a low glass transitiontemperature (Tg) as measured according to Diffferential ScanningCalorimetry (DSC). For moderate climates, the Tg of the syntheticpolymer fiber material is preferably less than 30° F. (−1° C.), forcolder climates, the Tg is preferably less than 0° (−18° C.), for evencolder climate the Tg is preferably less than −20° F. (−29° C.), andmore preferably less than −40° F. (−40° C.).

[0014] Suitable synthetic polymeric fiber materials include suchpolymers as polyolefins, vinyl copolymers, polyethers (e.g. polyamides),polyacrylates (i.e. acrylic polymers), styrene-acrylonitrile copolymers,polyesters, polyurethanes, tetrafluoroethylene, and copolymers thereof.The synthetic polymeric fiber is preferably comprised of polyester,polypropylene, tetrafluoroethylene, and copolymers thereof. Although thefiber length may range from about 3 mm to 40 mm, the synthetic polymericfibers preferably have a fiber length of at least 6 mm (6000 microns,0.24″) and more preferably a length of at least 10 mm.

[0015] The pavement marking composition comprising the syntheticpolymeric fibers within a polymeric material in combination with otheroptional ingredients such as retroreflective elements (e.g. glassbeads), filler, pigment, etc. preferably exhibits certain properties. Inone aspect the pavement marking composition is conformable. The abilityof the marker to conform to gross defects, such as deep cracks or otherdepressions commonly present on a pavement surface, can provide asubstantial durability advantage over preformed adhesive tapes. Ingeneral, the composition of the invention has a downweb and crosswebtear strength of at least 2.5 kilograms per square centimeter at 25° C.when measured according to ASTM 1938. Further, the ratio of the downwebaverage tear strength of the pavement marking sheet to crossweb tearstrength preferably ranges from 0.5 to 2 and more preferably ranges from0.7 to about 1.3.

[0016] Alternatively or in addition thereto, the pavement markingexhibits improved cold temperature properties. The cold temperatureproperties can be evaluated by extruding the composition into a 4 inchwide (101 mm) strip having a thickness of 1 to 2 mm. The sheet can thenbe conditioned at the temperature of interest for 4 hours. Immediatelyafter removing the sheet from the conditioning chamber the sheet isstruck with a hammer. Poor cold temperature properties is indicated bythe sheet breaking into pieces. Good cold temperature properties isindicated by the sheet remaining intact in a single piece, althoughcracking may be evident. Upon inspection one can typically see thefibers in the cracks.

[0017] The pavement marking composition generally comprises at least 0.1weight-% synthetic polymeric fiber, but no more than about 20 weight-%.Typically, the amount of synthetic polymeric fiber is less than 10weight-%, preferably less than 5 weight-% and more preferably less than2 weight-%, and even more preferably about 1 weight-% or less. Theamount of synthetic polymeric fiber is preferably at least 0.2 weight-%and more preferably at least about 0.3 weight-%. The amount of polymericmaterial preferably ranges from about 10 weight-% to about 85 weight-%.The pavement marking composition may optionally comprise up to about 75weight-% of other ingredients selected from reflective elements (e,g,glass beads), extender resins, fillers and pigment. Further, in additionto the synthetic polymeric fibers, the pavement marking composition mayfurther comprise other fibers such as inorganic fiber or other syntheticpolymeric fibers, provided the presence of such does not detract fromthe intended properties. Preferably, the pavement marking composition isfree of glass fibers.

[0018] The thermoplastic polymeric material provides a viscoelasticcharacter, which permits absorption of the forces and pressures ofwheeled road traffic without creating internal forces that tend toremove the marking from the roadway. Typically, a hydrocarbon or alkydthermoplastic material is employed. Preferred hydrocarbon thermoplasticmaterials include acid containing ethylene copolymers. Representativeacid containing ethylene copolymers include ethylene acrylic acid (EAA)copolymers and ethylene methacrylic acid (EMAA) copolymers, and mixturesof EAA and EMAA; as well as ionically cross-linked EMAA. Alternativethermoplastic materials, although less preferred for the topmost layer,include ethylene n-butyl acrylate (EnBA), ethylene vinyl acetate (EVA)and blends thereof, as well as polyolefins. Particularly preferredthermoplastic materials include EMAA polymer commercially available fromthe E. I. Dupont de Nemours and Company (Dupont) of Wilmington, Del.under the trade designation “NUCREL” and ionically cross-linked ethylenemethacrylic acid (EMAA) ionomers available from Dupont under the tradedesignation “Surlyn”. Other suitable thermoplastic materials suitablefor thermoplastic pavement markings as described in U.S. Pat. No.6,217,252 (Tolliver); incorporated herein by reference. Although thisreference relates to flame-sprayed pavement markings, the polymericmaterials (i.e. binders) described therein would also be suitable forconventional thermoplastic-based pavement marking applications methods.Polymeric materials described therein include acrylic polymers andcopolymers, olefin polymers and copolymers preferably having a numberaverage molecular weight greater than about 10,000, urethane polymersand copolymers, curable epoxy resins, ester polymers and copolymers, andblends thereof. For improved cold temperature performance, it issurmised that the pavement marking is based on a thermoplastic materialhaving a low glass transition temperature as previously described withregard to the fiber material.

[0019] Fillers are generally included in the composition at least forthe purpose of enhancing the visibility of the exposed top layer.However, fillers also advantageously enhance properties such asreinforcement, extending, surface hardness, and abrasion resistance.Platelet fillers, i.e., fillers having a plate-like shape, such asmagnesium silicate, talc, or mica, have been found to contribute thebest abrasion resistance and downweb strength properties. Also theplatelet fillers make the sheet material harder, which contributes tomaintaining a white appearance on the roadway. In addition, the plateletfillers have a high ratio of surface area to volume, which enhancestheir reinforcing ability. Magnetite particles such as strontiumplatelet fillers may also be employed. Such platelets become aligned ina north south orientation such that high magnetic strength can beachieved for magnetic lane awareness markings. Such markings aredescribed in greater detail in copending U.S. patent application Ser.No. 10/039654 filed Dec. 31, 2001; incorporated herein by reference.Other fillers, such as needle-type or bead-type fillers, may be employedinstead of or in addition to low concentrations of platelet fillers. Theamount of filler included in the sheet material of the invention varieswith the kind of filler used. Preferably, at least 3 weight-% ofplatelet fillers are used. With lower amounts of synthetic polymericfibers, higher amounts of filler are typically desired though fillers inan amount of more than 50 weight-% tend to stiffen the productexcessively. Preferably, the amounts of filler ranges from about 5 andabout 20 weight-%.

[0020] Retroreflective elements (e.g. transparent microspheres,cube-corner particles derived from ground sheeting) or andskid-resisting particles (e.g. sand particles) are also preferablyincluded in the pavement marking composition at concentration up toabout 45 weight-% to provide reflectivity at night and to give the sheetmaterial skid-resisting qualities. Preferably, about 25 weight-% toabout 40 weight-% reflective glass beads are dispersed throughout thethickness of the pavement marking sheet. An exterior layer of suchparticles may be provided on the top of the sheet material, partiallyembedded in the sheet material and partially protruding from the sheetmaterial, to provide immediate reflectivity and skid-resistance; andother particles may be embedded in the sheet material to become exposedas the sheet material is worn away. The particles may be held in thepartially protruding position by use of a support film adhered to thesheet material of the invention, for example, as taught in column 4 ofU.S. Pat. No. 4,988,541; incorporated herein by reference.

[0021] Typically the synthetic polymeric fibers are dry blended with thepolymeric material and other optional ingredients forming a relativelyhomogeneous mixture. The mixture can be supplied in either a granularform or is the form of a block. Various apparatus are commerciallyavailable for receiving such forms. Such apparatus heat and agitate thethermoplastic composition until melted and then transfer the meltedcomposition into a screed, ribbon or spray device wherein it is thenshaped into the specified width and thickness as a line, legend orsymbol. When applied on asphaltic pavement, the thermoplastic markingmaterial typically forms a sufficient thermal bond via heat fusion. Whenapplied to Portland concrete cements or on oxidized or aged asphalticpaved surfaces, application of a primer is recommended in order that asufficient mechanical bond is achieved.

[0022] Following application, the marker should be allowed to cool sothat the solidified binder material becomes tack-free. Adequate adhesionof the marker to the transportation surface can be evaluated in avariety of ways. Exposure to normal environmental or traffic conditionsfor a period of time, e.g., one day or more, will give the most reliabletest results. However, relatively simple tests such as a boot scuff testor attempting to remove the marker with a putty knife will often besufficient to determine whether marker has adhered adequately to thetransportation surface. In cases where the marker has been applied toasphalt, it may be necessary to allow the asphalt to cool for severalhours or more before evaluating adhesion. Asphalt can retain significantheat from the preheating step and may undergo cohesive failure withinthe asphalt if marker adhesion is tested too soon after the marker hasbeen applied.

[0023] Similarly, the composition can be extruded onto a release paperforming a sheet for the purpose of evaluating properties such asconformability and cold temperature properties of the pavement markingcomposition. Further, the composition may be employed in a pavementmarking tape as a conformance layer, such as described in U.S. Pat. No.5,194,113 (Lasch et al.).

[0024] Conformability of a marking can be evaluated in other ways aswell. One simple way is to press a layer or sheet of the material byhand against a complex, rough, or textured surface such as a concreteblock or asphalt composite pavement, remove the sheet, and observe thedegree to which the surface has been replicated in the sheet. Anotherassessment of the conformance of a marking tape may be obtained asfollows. First, the force required to deform the sheet material asuitable amount is measured. Second, a portion of the induced strain isrelieved. Finally, the retractive force remaining in the material at thereduced strain level is measured. A specific example of this processwould be to deform a sample to 115% of its original length by stretchingthe sample at a strain rate of 0.05 sec⁻¹ and measuring the stress at115% deformation, release the strain at the same rate, allow thematerial to return to 110% of its original length, and measure theretractive force. This measurement may be made using a standard tensiletesting apparatus such as, for example, the servohydraulic tensiletesters available from MTS Systems Corporation of Minneapolis, Minn.Preferred comformable materials exhibit a force to deform the sample to115% of its original length of less than 35 NT per cm width (20 lbs perinch width), and a retractive force at a subsequent 110% deformation ofless than 14 NT per cm width (8 lbs per inch width), although lesserforces are even more preferred. Other measures of conformability aredescribed in U.S. Pat. No. 5,194,113, and may also be used inconjunction with the pavement marking tapes of the present invention toevaluate conformance of a sheet material to an irregular surface.

[0025] The pavement marking preferably has good abrasion resistance asmay be indicated by a modified Taber abrasion test. The test uses anH-22 Taber abrader wheel, with a one kilogram weight on the wheel. Thetest specimen is held under water, and the abrader wheel passed over thespecimen for 500 cycles. Sheet material of the invention generallyexhibits a loss of no more than about 5 grams in this test.

[0026] Objects and advantages of the invention are further illustratedby the following examples, but the particular materials and amountsthereof recited in the examples, as well as other conditions anddetails, should not be construed to unduly limit the invention. Allpercentages and ratios herein are by weight unless otherwise specified.

EXAMPLES

[0027] Table I, as follows, identifies the chemical description, tradedesignation, supplier and location for each of the ingredients employedin the examples. TABLE I Chemical Description Trade Designation SupplierLocation Ethylene Acrylic “AC 5120” Allied Signal Morristown, NJ AcidCopolymer TiO₂-Pigment “TI PURE 960” DuPont Wilmington, DE MagneticFiller “UHE-9” Fermag Edison. NJ Industries Polyester Fiber (¼″)“6-3025-¼” Mini Fibers Johnson City, (½″) “6-3025-½” Inc. TN Glass Fiber“731A-16-W-¼”) Owens Corning Toledo, OH

[0028] Table II as follows sets forth the weight percentage of eachingredient employed in Comparative Example A, and Examples 1-2. TABLE IIComparative Example 1 Example 2 Example A Trade Designation 81.9 81.981.9 “AC 5120” 17.7 17.7 17.7 “TI PURE 960”  0.4 — — “6-3025-¼” — 0.4 —“6-3025-½” — — 0.4 “731A-16-W-¼”

[0029] The materials were dry blended in gallon jars. The mixture washeated on a hot plate until the temperature reached 305° F. (152° C.)and poured into a heated (300° F./152° C.) extrusion head that deliversthe mixture unto silicone release paper forming a 1-2 mm thick 4″(101mm) wide tape.

[0030] For each of the examples the tear strength was evaluatedaccording to ASTM D1938. Table III, as follows sets forth the testresults: TABLE III Comparative Example 1 Example 2 Example A Down WebAverage 2.49 2.26 3.13 Tear Lb (kg) (5.48) (4.97) (6.89) Cross WebAverage 2.39 2.98 1.89 Tear Lb (kg) (5.26) (6.56) (4.16) Ratio-Down Web1.04 0.76 1.65 Tear/Crossweb Tear

[0031] The results show that the ratio of down web tear to crossweb tearof the synthetic polymeric fiber containing extruded sheet isconsiderably closer to 1 than the composition comprising glass fibers.Further the ½″ synthetic polymeric fiber contributes a higher crosswebtear strength, particularly in comparison with the glass fibers.

[0032] Examples 1 and 2 and Comparative Example A were conditioned for 4hours at −40° F. The sample were removed from the freezer and struckwith a hammer. Comparative Example A shattered into several pieces.Examples 1 and 2 cracked, yet the pieces did not separate along thecrack.

[0033] Prepared in the same manner, Table III as follows sets forth theweight percentage of each ingredient employed in Comparative Example B,and Examples 3-5. TABLE III Comparative Example 3 Example 4 Example 5Example B Trade Designation 39.42 39.26 39.18 39.4 “AC 5120” 17.7 17.717.7 “UHE-9” 0.394 0.785 .98 — “6-3025-¼”

[0034] The cold temperature properties of these samples were evaluatedin the same manner at −10° F. Comparative Example B shattered; whereasExamples 3-5 cracked yet remained intact.

What is claimed is:
 1. A pavement marking composition comprisingsynthetic polymeric fibers dispersed within a thermoplastic-basedpolymeric material, wherein the synthetic polymeric fibers have a meltpoint greater than the polymeric material.
 2. The pavement marking sheetof claim 1 wherein the fibers are randomly dispersed within thepolymeric material.
 3. The pavement marking composition of claim 1wherein the synthetic polymeric fibers have a melt point greater than400° F.
 4. The pavement marking composition of claim 1 wherein thesynthetic polymeric fibers are selected from the group comprisingpolyester, polyamide, polypropylene, tetrafluoroethylene and copolymersthereof.
 5. The pavement marking composition of claim 1 wherein saidcomposition is provided as a sheet having a thickness ranging from about0.25 mm to about 5 mm, said sheet having a downweb direction andcrossweb direction.
 6. The pavement marking sheet of claim 5 wherein thesheet is conformable.
 8. The pavement marking sheet of claim 5 whereinthe downweb direction and crossweb direction has a tear ratio thatranges from 0.5 to 2 when measured according to ASTM
 1938. 9. Thepavement marking sheet of claim 5 wherein the downweb direction andcrossweb direction has a tear ratio that ranges from 0.7 to 1.3 whenmeasured according to ASTM
 1938. 10. The pavement marking composition ofclaim 1 wherein the synthetic polymeric fiber ranges from about 0.2weight-% to about 2 weight-%.
 11. The pavement marking of claim 1wherein the polymeric material is selected from the group comprisingalkyd thermoplastic and hydrocarbon thermoplastic.
 12. The pavementmarking of claim 11 wherein the polymeric material is a hydrocarbonthermoplastic.
 13. The pavement marking of claim 12 wherein thepolymeric material comprises an acid containing copolymer of ethylene.14. The pavement marking composition of claim 1 wherein the compositioncomprises other ingredients selected from the group comprisingreflective elements, extender resins, fillers, and pigments.
 15. Thepavement marking of claim 1 wherein the composition comprises magneticparticles.
 16. The pavement marking composition of claim 1 wherein thesynthetic polymeric fibers have a fiber length of at least 6 mm.
 17. Thepavement marking composition of claim 1 wherein the synthetic polymericfibers have a fiber length of at least 10 mm.
 18. A method of making apavement marking comprising: providing a composition comprising athermoplastic-based polymeric material and synthetic polymeric fibers;heating the composition to a temperature wherein the composition isextrudeable and the synthetic polymeric fibers are unmelted; andextruding the composition on a pavement surface.
 19. A method of makinga pavement marking comprising: dry blending a thermoplastic polymer andsynthetic polymeric fibers; melting and mixing the blend; and extrudingthe blend onto a pavement surface at a temperature less than the meltpoint of the synthetic polymeric fibers.